Organic foods, by definition, can’t knowingly contain genetically modified organisms, known as GMOs. But genetically modified corn, soy and other crops have become such common ingredients in processed foods that even one of the nation’s top organic food retailers says it hasn’t been able to avoid stocking some products that contain them.

“No one would guess that there are genetically engineered foods right here in Whole Foods,” said Alexis Baden-Mayer, political director of the Organic Consumers Association, which organized the protest. The activists dramatically trashed a battery of well-known health food brands outside the store, including Tofutti, Kashi and Boca Burgers.

Though people have been modifying foodstuffs through selective breeding and other methods for centuries, genetically modified crops differ in that the plants grow from seeds in which DNA splicing has been used to place genes from another source into a plant. In this way, the crop can be made to withstand a weed-killing pesticide, for example, or incorporate a bacterial toxin that can repel pests.

Some consumers are concerned that such changes may pose health risks and say manufacturers should be required to prove GMOs are safe for human consumption before putting them on the market. They also say products containing genetically modified ingredients should be identified for the consumer; the U.S. is one of the few industrialized nations that does not require such labeling or testing.

Industry representatives say that GMOs are safe and that labeling them is unnecessary, citing a 1992 statement from the FDA saying the agency had no reason to believe GMOs “differ from other foods in any meaningful or uniform way.” No mainstream regulatory organization in the U.S. has opposed the introduction of GMOs.

“FDA has the scientific and nutrition expertise to establish food labeling and to assess food safety,” said Ab Basu, the Biotechnology Industry Organization‘s acting executive vice president for food and agriculture. “You can look at the FDA website and see that if the corn is substantially equivalent to corn produced conventionally, there is no reason to label it as being any different.”